Control for blast furnaces



Nov. 30, 1965 R. R. SWAIN 3,220,825

CONTROL FOR BLAST FURNACES Filed June 1. 1961 2 Sheets-Sheet l mu) x z40 CD 23 i J 10 a N I) a J- v Ll.

g a 5* J 2 TOTAL COMBUSTIBLES ANALYSER INVENTOR.

RALPH R. SWAIN ATTORNEY 1955 I R. R. SWAIN 3,220,825

' CONTROL FOR BLAST FURNACES Filed June 1, 1961 2 Sheets-Sheet 2 &9 v lPLJRGE AIR S;

TO OTHER TUYERES 48A l8 FROM BLAST GAS BLOWER BUSTLE PIPE D B A g 5| 0 IINJECTION H i & FUEL I l L 48 INVENTOR. B A RALPH R. SWAIN ATTORNEYUnited States Patent 3,220,825 CONTROL FOR BLAST FURNACES Ralph R.Swain, South Euclid, Ohio, assignor to Bailey Meter Company, acorporation of Delaware Filed June 1, 1961, Ser. No. 114,090 16 Claims.(CI. 7542) This invention relates to the control of blast furnaces usedin the production of pig iron from iron ore.

The conventional blast furnace comprises an elongated section known asthe stack, a lower section known as the hearth and an intermediatesection known as the bosh located between the hearth and the stack. Ablast gas, usually compressed air, is blown through tuyeres into theupper portion of the hearth, and the burden, including limestone,ferrous bearing material and a carbonaceous material such as coke isintermittently charged into the furnace at the top of the stack. Theburden moves down the stack. In the zone adjacent the tuyeres the cokeor other carbonaceous material burns and the heat of combustion smeltsthe ore to produce molten pig iron. The products of combustion, as theypass upwardly through the stack, being at relatively high temperatureserve to preheat the burden and reduce the iron ore.

The gaseous products of combustion are discharged from the top of theblast furnace through one or more offtake pipes and are commonlyreferred to collectively as top gas or blast furnace gas. Thecomposition of this gas may vary considerably; however, typically itwill be composed of approximately combustibles, largely hydrogen andcarbon monoxide, with the balance carbon dioxide, nitrogen and watervapor.

In the operation of a blast furnace it is not uncommon to experienceerratic operation. Once such erratic operation occurs it is difi'icultto restore normal operation because a change in the burden, which is theprincipal adjustment available, requires a number of hours to beeffective. While the amount of hot blast can be changed in a directionto restore normal operation, practically the amount of adjustment whichcan be made is limited due to the effect on pig iron and flue dustproduction.

The recently introduced practice of enriching the blast gas with oxygenas a means of increasing pig iron production has tended to accentuatethe problem as the increased rate of downward movement of the burdencauses it to be insutficiently heated before reaching the hearth. Inattempting to correct for this condition an over-correction orunder-correction is frequently made. Because of the dead time between anadjustment and the adjustment becoming effective, the furnace may beplaced in a cycling condition which cannot be attenuated in anyreasonable period of time and while existing results in poor productionand generally unsatisfactory performance.

A further recently introduced practive involves the introduction of asupplementary fuel, known as an, injection fuel into the hearth alongwith the blast gas. This fuel, which may be a gas, such as natural gasor coke oven gas, or a fuel oil, has been found to increase iron outputand decrease the amount of coke or other carbonaceous material required.A fairly comprehensive report on the practice is to be found in anarticle entitled, Fuel Injection Increases Blast Furnace Iron Output,beginning on page 112 of the Dec. 5, 1960, issue of the publicationSteel.

I have found that this fuel may also be used to stabilize blast furnaceoperation, resulting in increased production, higher quality product,higher operating eficiency and lower maintenance. In accordance with myinvention the rate of flow of injection fuel is controlled to maintain apredetermined combustibles content in the top gas. I have found that anyupset in the operation of a blast ice furnace is reflected immediatelyby a corresponding change in the composition of this gas. I have furtherfound that the injection fuel provides a corrective agent immediatelyeffective to restore the furnace to normal operation. Thus I may say usethe combustibles content of the top gas as an index of furnace operationand the injection fuel as a corrective agent to maintain the index at apredetermined or desired value. The long dead time formerly existingbetween the taking of a corrective measure and the effect of thatmeasure being felt is eliminated to the end that the furnace may becontinuously maintained at the point of optimum operation.

In the drawings:

FIG. 1 is a schematic illustration of a control system incorporating myinvention.

FIGS. 2 and 3 illustrate modifications which may be incorporated in thecontrol system shown in FIG. 1.

Referring to FIG. 1, I therein show a blast furnace 1 having a stack 2which at the top is provided with a large hell 3 and a small hell 4through which the burden is charged into the furnace. At the lower endof the furnace there is a hearth 5 separated from the stack 2 by a bosh6. A bustle pipe 7 encircles the lower portion of the furnace forsupplying blast gas under pressure to the hearth. The blast gas isadmitted to the furnace through a plurality of tuyeres 8, connected tothe bustle pipe 7 by means of pipes 9. The molten slag and iron collectsin the hearth and is periodically tapped from the furnace throughsuitable tap holes (not shown).

As previously described, the blast gas burns the carbonaceous material,of which the burden is partially composed, in the vicinity of the hearthand the products of combustion pass upwardly through the stack and aredischarged through one or more off-take pipes such as shown at 10.

The blast gas, obtained from the atmosphere, after passing through asuitable filter (not shown) to remove dust and dirt and being enrichedwith oxygen as is sometimes done in modern practice passes through asuction conduit 11 to a large capacity blower 12 driven by a motor 13.The blast gas is discharged from the blower 12 through conduit 14 into astove 15 in which it is preheated. Usually at least three stoves, suchas I have shown at 15, are provided for each blast furnace. In customarypractice two stoves are being heated, usually by burning the top gasfrom the blast furnace, while the third is preheating the blast gas.This operation is rotated, one stove after another being used to preheatthe blast gas while the remaining two are being heated therebymaintaining the blast gas at a fairly uniform temperature.

A by-pass line 16 is ordinarily placed around each stove so that theblast gas leaving the stove 15 may be tempered with unheated gas. Avalve 17 either manually or automatically controlled, as later to bedescribed, is provided in the by-pass line so that the amount oftempering gas may be adjusted as required to maintain a desired constanttemperature of the hot blast which may, for example, be in the order of1000 F. From the stove 15 the blast gas is transported to the bustlepipe 7 through a conduit 18.

The injection fuel, obtained from any suitable source (not shown) isintroduced by way of pipe 20 into a header 19 encircling the blastfurnace. I have, for purposes of illustration, shown an arrangement forthe use of fuel oil as the injection fuel. Obvious modifications inregard to pipe sizes, header arrangement and the like would be made inthe event another fuel such as natural gas or coke oven gas was used asthe injection fuel. The injection fuel is discharged through each tuyereby a suitable burner arrangement such as I have diagrama 3 maticallyshown at 21 which is connected to the header by pipe 22.

Turning now to a consideration of control for the blast furnace 1 Iillustrate a system of the pneumatically operated type for the reasonthat the components of such type are well known and understood in theart. However, I could equally as well use for illustrative purposes anelectrically or hydraulically operated control system as will be readilyappreciated as the description proceeds.

In FIG. 1 I show a constant flow control for the blast gas. Therein aflow controller diagrammatically illustrated at 25 establishes a loadingpressure proportional to the rate of flow of blast gas which istransmitted through a pipe 26 to the B chamber of a relay 27. This relaymay, for example, be of a type illustrated and described in UnitedStates Patent 2,805,678 issued to Michael Panich on Sept. 10, 1957, andestablishes at ports D a control pressure varying both in accordancewith changes in the loading pressure in pipe 26 and the time integral ofthe deviation of this pressure from a predetermined value correspondingto the desired rate of flow of blast gas in conduit 11. Such a relay isspoken of in the art as having proportional plus reset action. Both theproportional and reset actions may be adjusted in accordance with thetime constants of the system by means of sector 28 and bleed valve 29respectively.

The control pressure is transmitted to a Manual-Automatic SelectorStation 30 through pipe 31 and thence by way of a pipe 32 to a controlunit 33 for the motor 13. The control unit 33 may take any conventionalform and serves to regulate the speed of motor 13 and accordingly ofblower 12 in accordance with the magnitude of the control pressure inpipe 32..

The Selector Station 30'and other Selector Stations in the controlsystem may be of the type illustrated and described in the Panich Patent2,805,678 and afford a means for transferring the control from Automaticto Remote Manual. Thus there is provided a knob 34 by which the controlpressure in pipe 32 may be manually adjusted with the Station in ManualPosition. With the Station .in Automatic Position the Set Point, thatis, the rate of flow maintained by the control may be adjusted by a knob35 which establishes a pressure transmitted through a pipe 36 to the Abellows of relay 27 and against which the loading pressure establishedby transmitter 25 is balanced. The Selector Station 30 is also providedwith a pneumatic switch 37 for transferring the control from Automaticto Manual and vice versa.

In accordance with my invention the rate of flow of injection fuel isregulated to maintain a predetermined total combustibles in the top gas.While I show and prefer to use the total combustibles in the top gas asthe control index, a particular constituent of the gas such as hydrogen,carbon monoxide or carbon dioxide may in some circumstances be employedas there may in some cases be a fixed ratio between a particularcombustibles constituent and the total combustibles. In employing theterm combustibles it is to be understood that in its broader aspects itcomprehends one, more than one or all of the combustible constituents inthe top gas. By combustibles content I mean the percent by volume orpercent by weight of a unit volume or unit weight of the top gas.

I show at 38 a combustibles controller for establishing a loadingpressure proportional to the combustibles in the top gas leaving theblast furnace through off-take pipe 10. This loading pressure istransmitted through a pipe 39 to a relay 40, similar to the relay 27,and incorporating proportional plus reset action. The control pressureestablished at port D of this relay is transmitted through a pipe 41 toa Selector Station 42 and thence to a relay 43 through a pipe 44. Inrelay 43 (which may be of a type illustrated and described in PanichPatent 2,805,678) changes in pressure at output port D are producedinversely proportional to changes in pressure at inlet port B, thus anincrease in pressure at B will produce a corresponding decrease inpressure at port D and vice versa. An adjustment 45 is provided foradjusting the ratio between changes at B and resulting changes at D.This is spoken of in the art as a, proportional band adjustment.

While the control pressure established at port D of relay 43 could actdirectly on control valve 46 to adjust the rate of fiow of injectionfuel, I prefer, in accordance with well established principles in thecontrol art, to have this loading pressure adjust the Set Point of aconstant flow control of the injection fuel. Thus I show a flowcontroller 47 for establishing a loading pressure proportional to therate of flow of injection fuel which by means of a relay 48 havingproportional plus reset action, maintains a constant rate of flow ofinjection fuel. The Set Point of this control is adjusted from thecombustibles in the top gas by introducing the control pressureestablished by relay 43 through a pipe 49 into the A bellows of relay48. Thus the rate of flow of injection fuel is varied to maintain theloading pressure established by flow controller 47 in balance with thecontrol pressure established by relay 43 to the ultimate end that therate of flow of injection fuel is adjusted as required to maintain aconstant combustibles content in the top gas. A Selector Station 50provides a means for remote Manual control of the valve 46.

To anticipate changes in the combustibles content of the top gasoccasioned by changes in the rate of flow of blast gas and therebyprovide a closer control, the loading pressure established by flowcontroller 25 is transmitted through a branch pipe 26A to the A bellowsof relay 43. Changes in this loading pressure will thus producecorresponding changes in the control pressure produced by relay 43 andin the rate of flow of injection fuel. Changes in the combustiblescontent of the top gas which would otherwise occur by virtue of changesin the rate of flow of blast gas and which the control from combustiblescontent would be called upon to correct are thereby avoided.

In FIG. 1, as described, I show a constant flow control of the totalinjection fuel. In the usual application this is satisfactory, however,as can be appreciated even with the total flow maintained as desired,objectionable variations may occur in the flow of each individual tuyereoccasioned by variations in the relative resistance to flow and thelike. A minor modification may readily be incorporated in the control asillustrated in FIG. 1, and which I have shown in FIG. 2 to assure theflow to each individual tuyere being maintained at the desired value.Therein I have shown my modified control applied to one tuyere, it beingunderstood that a similar control would be provided on every othertuyere through which injection fuel is admitted to the blast furnace.

In the modification shown in FIG. 2 a constant flow controller 47Aestablishes a loading pressure corresponding to the rate of flow ofinjection fuel to the burner 21. This loading pressure by means of arelay 48A maintains this flow constant at a value determined by thecontrol pressure admitted into the A bellows and generated in relay 43as described with reference to FIG. 1. Thus changes in the relativeresistance to flow and the like will not affect the uniform discharge ofinjection fuel through the tuyeres as the constant flow controlassociated with each tuyere will adjust its valve 46A to maintain therate of flow to the tuyere at a value established by the relay 43.

I have mentioned with respect to the description relating to FIG. -1that the preheated blast gas is usually maintained at a desiredtemperature by adjusting the flow through a by-pass line around thestove. In FIG. 3, I have shown a typical arrangement wherein atemperature controller 50 responsive to the temperature of the preheatedblast establishes a corresponding loading pressure which is introducedinto the A chamber of relay 51 having a proportional plus reset action.The relay 51 produces a control pressure which is transmitted through apipe 52 to a diaphragm operated valve 17A disposed in the by-pass line16. The arrangement is such that an increase in temperature in conduit18 causes a corresponding increase in flow through the by-pass line 16and a continuing change in this flow proportional to the deviation inthis temperature from Set Point value and in sense dependent upon thesense of the deviation.

As I have found that the temperature of the preheated blast gas may bedesirably modified with changes in the rate of flow of injection fuel, Ifurther show in FIG. 3 the Set Point of the temperature control adjustedfrom the rate of flow of injection fuel. Such a modification may bedesirable to compensate for the cooling effect of the injection fuel onhearth temperature and other effects on the blast furnace which changesin the rate of flow of injection fuel may have. Referring to FIG. 3 Ishow the loading pressure established by flow controller 47 introducedinto the B chamber of relay 51 through a pipe 53. Accordingly the relay51 will act to vary the flow through the by-pass line 16 as required tomaintain the loading pressure established by the temperature controller50 in balance with the loading pressure introduced into the B chamber byway of pipe 53 to the ultimate end that the Set Point, or in other Wordsthe temperature in conduit 18 is maintained at a value established bythe rate of flow of injection fuel.

The present invention thus provides a novel method and apparatus forcontrolling the operation of a blast furnace. Although only one basicembodiment of the invention has been disclosed and described herein, itis expressly understood that various changes and substitutions may bemade without departing from the spirit of the invention. Reference willtherefore be had to the appended claims for a definition of the limitsof the invention.

What I claim as new and desire to obtain by Letters Patent of the UnitedStates is:

1. The method of controlling a blast furnace having an elongatedvertical stack into the top of which a burden consisting essentially oflimestone, a carbonaceous material and a ferrous bearing material ischarged and a lower hearth section into which a blast gas and aninjection fuel are discharged and burned the hot gases of combustionpassing up through the stack for the reduction of the iron ore to ironwhich includes regulating the flow of the injection fuel in accordancewith the combustibles content in the top gas leaving the furnace.

2. The method in accordance with claim 1 wherein the rate of flow of theinjection fuel is regulated to maintain a predetermined constantcombustibles content in the top gas leaving the furnace.

3. The method in accordance with claim 2 including the further steps ofmaintaining the rate of flow of injection fuel constant and adjustingthe constant rate maintained as required to maintain the predeterminedconstant combustibles content in the top gas leaving the furnace.

4. The method of claim 3 including the further step of adjusting thetemperature of the blast gas in accordance with the rate of fiow ofinjection fuel.

5. The method of claim 3 including the further step of increasing thetemperature of the blast gas in proportion to increases in the rate offlow of the injection fuel and vice versa.

6. The method of claim 5 including the further step of maintaining therate of flow of blast gas to the furnace constant.

7. The method of controlling a blast furnace having a vertical elongatedstack into the top of which a burden consisting essentially oflimestone, a carbonaceous material and a ferrous bearing material isperiodically charged and a lower hearth section into which a blast gasand an injection fuel are continuously discharged through a plurality oftuyeres surrounding the hearth section and burned, the hot gases ofcombustion passing up through the stack for the reduction of iron ore toiron which in- 6 cludes maintaining the rate of flow of injection fuelto each of the plurality of tuyeres constant and adjusting the constantrate of flow maintanied as required to maintain the combustibles contentin the top gas leaving the furnace constant at a predetermined value.

8. The method of claim 7 wherein the rates of flow of all the tuyeres isadjusted in parallel to maintain the combustibles content at apredetermined value.

9. The method of controlling a blast furnace having a vertical elongatedstack into the top of which a burden consisting essentially oflimestone, a carbonaceous material and a ferrous bearing material isperiodically charged and a lower hearth section into which a blast gasand an injection fuel are continuously discharged through a plurality oftuyeres adjacent the hearth section and burned, the hot gases ofcombustion passing through the stack for the reduction of iron ore toiron which includes, measuring the rate of flow of injection fuel toeach tuyere, utilizing the measurements to maintain the rate of flow toeach tuyere constant, measuring the combustibles content of the top gasleaving the furnace and simultaneously adjusting the rate of flow ofinjection fuel to all of the tuyeres as required to maintain the measureof combustibles content at a predetermined value.

10. In a control system for a blast furnace for the reduction of ironore to iron having an elongated vertical stack into the top of which aburden consisting of carbonaceous material, limestone and a ferrousbearing material is charged and a lower hearth section into which ablast gas and an injection fuel are discharged and burned, comprising,in combination, means for establishing a control signal corresponding tothe combustibles content in the top gas leaving the furnace, and meansfor regulating the flow of injection fuel to the furnace responsive tosaid signal.

11. In a control system for a blast furnace for the reduction of ironore to iron having an elongated vertical stack into the top of which aburden consisting of a carbonaceous material, limestone and a ferrousbearing material is charged and a lower hearth section into which ablast gas and an injection fuel are discharged and burned, comprising incombination constant flow control means of the injection fuel having anadjustable set point, means responsive to at least one of thecombustibles constituents in the top gas leaving the furnace and meansunder the control of said last named means for adjusting said set pointto maintain said combustibles constituent at a predetermined value.

12. In a control system for a blast furnace for the reduction of ironore to iron having an elongated vertical stack into the top of which aburden consisting of a carbonaceous material, limestone and a ferrousbearing material is charged and a lower hearth section into which ablast gas and an injection fuel are discharged and burned, comprising incombination, means for heating the blast gas, means for controlling theheating means to maintain the temperature of the blast gas entering thefurnace at a constant value and means for adjusting the constant valuein accordance with the rate of flow of injection fuel into the furnace.

13. In a control system for a blast furnace for the reduction of ironore to iron having a vertical elongated stack into the top of which aburden consisting of limestone, :1 carbonaceous material and a ferroushearing material is charged and a lower hearth section into which ablast gas and an injection fuel are discharged and burned through aplurality of tuyeres surrounding the hearth section, comprising incombination, constant flow control means of the rate of flow ofinjection fuel to each tuyere having an adjustable set point, measuringmeans of the combustibles content of the top gas leaving the furnace andmeans under the control of said last named means for simultaneouslyadjusting the set points of all of the constant flow control means tomaintain the combustibles content in the top gas at a predeterminedvalue.

14. In a control system for a blast furnace for the reduction of ironore to-iron having a vertical elongated stack into the top of which aburden consisting of limestone, a carbonaceous material and a ferrousbearing material-is charged and a lower hearth section into which ablast gas and an injection fuel are discharged and burned, comprising incombination, regulating means of the rate of flow of injection fuel, ameter of the combustibles in the top gas leaving the furnaceestablishing a pneumatic loading pressure proportional to thecombustibles, a controller responsive to said loading pressuregenerating a control pressure varying in accordance with changes in theloading pressure and the time integral of the deviation of aid loadingpressure from a predetermined value and means operated by controlpressure for positioning said regulating means.

15. A control system according to claim 14 wherein the regulating meansis a constant flow control means having an adjustable set point and thecontrol pressure is effective for adjusting the set point.

16. A control system according to claim 15 including means formaintaining the temperature of the blast gas at a predetermined valuehaving an adjustable set point and also including means responsive tothe rate of flow of injection fuel for adjusting said set point to varythe temperature of the blast gas in accordance with changes in the rateof flow of injection fuel.

References Cited by the Examiner OTHER REFERENCES Blast FurnacePractice, page 107. Edited by Sweetser. Published in 1938, by theMcGraw-Hill Book Co., New York.

Blast Furnace, Coke Oven, and Raw Materials Proceedings, vol. 19, pages1, 279, 282 to 291, 297 to 300. Published in 1960 by the A.I.M.E., NewYork.

Fuel Injection Increases Blast Furnace Iron Output.

20 In Steel; 147 (23), December 5, 1960, pp. 112-116. TS

JOHN F. CAMPBELL, Primary Examiner.

25 RAY K. WINDHAM, JAMES H. TAYMAN, JR.,

Examiners.

1. THE METHOD OF CONTROLLING A BLAST FURNACE HAVING AN ELONGATEDVERTICAL STACK INTO THE TOP OF WHICH A BURDEN CONSISTING ESSENTIALLY OFLIMESTONE, A CARBONACEOUS MATERIAL AND A FERROUS BEARING MATERIAL ISCHARGED AND A LOWER HEARTH SECTION INTO WHICH A BLAST GAS AND ANINJECTION FUEL ARE DISCHARGED AND BURNED THE HOT GASES OF COMBUSTIONPASSING UP THROUGH THE STACK FOR THE REDUCTION OF THE IRON ORE TO IRONWHICH INCLUDES REGULATING THE FLOW OF THE INJECTION FUEL IN ACCORDANCEWITH THE COMBUSTIBLES CONTENT IN THE TOP GAS LEAVING THE FURNACE.
 10. INA CONTROL SYSTEM FOR A BLAST FURNACE FOR THE REDUCTION OF IRON ORE TOIRON HAVING AN ELONGATED VERTICAL STACK INTO THE TOP OF WHICH A BURDENCONSISTING OF CARBONACEOUS MATERIAL, LIMESTONE AND A FERROUS BEARINGMATERIAL IS CHARGED AND A LOWER HEARTH SECTION INTO WHICH A BLAST GASAND AN INJECTION FUEL ARE DISCHARGED AND BURNED, COMPRISING, INCOMBINATION, MEANS FOR ESTABLISHING A CONTROL SIGNAL CORRESPONDING TOTHE COMBUSTIBLES CONTENT IN THE TOP GAS LEAVING THE FURNACE, AND MEANSFOR REGULATING THE FLOW OF INJECTION FUEL TO THE FURNACE RESPONSIVE TOSAID SIGNAL.